System for the circulatory conveyance of media

ABSTRACT

The invention relates to a system for the circulatory conveyance of media, with a drive and with two conveying chambers, the first conveying chamber constituting a feed chamber and the second conveying chamber a return chamber.

[0001] The invention relates to a system for the circulatory conveyanceof media, in particular of coating masses, such as, for example, gluesand inks in the printing and packaging industry, between a first and asecond container and claims the priority of German patent application100 44 868.2-15 to the contents of which reference is made.

[0002] When a firmly adhering layer of originally formless material iscoated, that is to say applied to a workpiece, the homogeneity of thecoating mass is particularly important. The coating masses are thereforeoften circulated continuously between the stock or supply vessel andwhat is known as the doctor blade chamber. The doctor blade chamberconstitutes the laterally delimited space in which the inking orprinting rollers are provided with the coating medium. The doctor bladechamber advantageously has as constant a filling height as possible.

[0003] In order to make it possible for the coating mass to be appliedevenly to the rollers, it is advantageous, furthermore, to feed thecoating mass from the stock container into the doctor blade chamberwithout any pulsation, so that the formation of foam or of waves in thedoctor blade chamber is avoided.

[0004] For this purpose, it is known to convey the coating mass out ofthe stock container into the doctor blade chamber with the aid of acentrifugal pump. The disadvantage of these pumps, however, is that theyhave only a restricted regulating range which is determined by thethrottle curve of the pump. If the centrifugal pumps are notregenerative, they are often used as what are known as submerged pumps,that is to say the medium flows into the pump under gravity. The resultof this is that, during emptying, for example in the event of a productchange, a large residual quantity often remains in the stock container.

[0005] Centrifugal pumps have an electric drive. This electric driveconstitutes a considerable risk during coating, particularly withsolvent-containing media, for example solvent-based inks. To be precise,in order to counteract the risk of fire and explosion resulting from theuse of combustible materials, comprehensive safety measures arenecessary.

[0006] Moreover, centrifugal pumps, particularly in the form ofsubmerged pumps, are unwieldy when the coating baths are being changed,that is to say in the event of a product change.

[0007] Insofar as a centrifugal pump is used for feeding the coatingmedium into the doctor blade chamber, the discharge of the medium fromthe doctor blade chamber back into the stock container takes place bygravity. This means that the doctor blade chamber has to be arranged ata particular height in relation to the stock container, in order to makeoutflow possible. Furthermore, the discharge lines must have a widediameter, in order to ensure a sufficient return speed. Otherwise,precisely in the case of changing viscosities of different media, itwould not be possible to ensure a return which is sufficient forhomogenizing the medium.

[0008] This results directly in the disadvantage that the media withinthe discharge lines are exposed over a large area to the ambient air, sothat precisely solvent-containing coating masses give off gas. Thetendency of the medium to hardening and encrustation consequentlyincreases. The consequences of this are a lowering of the coatingquality and additional cleaning measures.

[0009] Moreover, there is the risk that the doctor blade chamber willrun empty in the event of a failure of the feed pump.

[0010] In order to counteract these disadvantages, it is known to equipthe coating systems with a separate recirculating pump.

[0011] In this case, however, there is a considerable difficulty incoordinating the performance values of the feed pump and recirculatingpump. Thus, to avoid any overfilling of the doctor blade chamber, it isnecessary for the performance of the recirculating pump always to bekept somewhat above that of the feed pump. This coordination isdifficult, however, particularly because a decrease of coating mediaoccurs in the doctor blade chamber due to the rollers, that is to say areduction in the coating medium must be taken into account. If theperformance of the recirculating pump is too high, however, the rollersand the doctor blade chamber may run dry.

[0012] The use of two different pumps for feeding the medium and fordischarging it from the doctor blade chamber therefore fundamentallyentails the risk of overfilling or running dry of the doctor bladechamber in the event of failure or of unintentional underconveyance oroverconveyance by one of the two pumps.

[0013] Proceeding from these disadvantages, the object on which theinvention is based is to provide a pump assembly which reliably andsafely ensures the feed of a medium from a first vessel into a secondvessel, with a medium being at the same time returned from the secondvessel into the first vessel.

[0014] This object is achieved by means of a pump assembly as claimed inclaim 1. Advantageous further developments are in each case the subjectmatter of the subclaims. T

[0015] he invention is based on the notion of using a pump system withtwo conveying chambers which have a common drive. In this case, one ofthe conveying chambers serves as a feed chamber, while the other chamberserves as a return chamber. This makes it possible to coordinate the twochambers automatically. In their function as a feed chamber or a returnchamber, the conveying chambers in each case have the necessaryconnections, lines and, if appropriate, valves, in order to convey themedium from a first container into a second container (feed chamber) andfrom this second container back into the first container (returnchamber).

[0016] In a particular embodiment, this pump assembly is adouble-diaphragm pump, the two conveying chambers of which are separatedfrom one another.

[0017] The particular advantage of using a common drive is thatinterlocking between the conveying chambers is largely superfluous,since, even if the drive fails, there is no fear either of dry runningor of overfilling of the vessel to be charged or to be emptied, that isto say of the doctor blade chamber where coating is concerned.Complicated valves or regulations for the purposes of coordinating thechambers with one another can also largely be dispensed with.

[0018] In order to prevent an overfilling of the doctor blade chamberreliably at any time, the conveying capacity of the return chambershould be slightly higher than that of the feed chamber. This isachieved in an advantageous embodiment, according to the invention, inthat the medium is first conducted into an integrated pulsation dampervia suction and delivery valves of the feed chamber. This pulsationdamper is preferably formed by an actively operating selfregulatingpulsation damper with its own air control, the supply of which isderived internally from the supply of the pump. Consequently, thepulsation damper can be adapted to the changing operating states of thepump, and the maximum possible pulsation damping is ensured at alltimes.

[0019] The following pulsation damper necessarily results in some lossof performance and therefore in a slight reduction in the feed quantity,while the return into the stock container can take place in an undampedmanner. This produces a ratio between return and feed to the benefit ofthe return, so that overfilling of the doctor blade chamber can bereliably avoided.

[0020] Furthermore, the advantage of the pulsation damper is that thefeed into the doctor blade chamber takes place in as pulsation-free amanner as possible and therefore a high quality of, for example, thecoatings becomes possible.

[0021] After leaving the pulsation damper, the medium advantageouslypasses through an integrated needle valve. The necessary conveyingquantity into the doctor blade chamber can thus be regulatedcontinuously and sensitively.

[0022] In a further embodiment, the return of the medium out of thedoctor blade chamber into the stock container can take place via areservoir, the volume of which corresponds to that of the displacementvolume of the diaphragms. This makes it possible largely to prevent thesituation where influences, for example turbulences, during the suctionstroke of the undamped return side disturb the liquid level in thedoctor blade chamber and have an adverse effect on the coating process.Moreover, the undamped return can assist the desired effect of theintermixing of the medium.

[0023] Since the pump assembly is also used for returning the mediuminto the stock container, the discharge line can be small and alsoflexible. This avoids one disadvantage of the prior art, in which theoutflowing medium is exposed over a large area to the ambient air due tolarge diameters of the discharge lines.

[0024] In an advantageous embodiment, the pump assembly according to theinvention may have a four-way valve which may be arranged on thedelivery side of the conveying chamber downstream of the pulsationchamber and of the needle valve. The conveying direction of the feedchamber is therefore reversed simply by a lever being changed over.Whereas, in normal conveying operation, the medium is sucked in andconveyed into the doctor blade chamber via a pulsation damper, by thisvalve being changed over the doctor blade chamber and the lines,including the pump chamber, can be sucked empty and the medium conveyedback into the stock container. The necessarily corotating return chambersimultaneously empties the line and the pump chamber. The entireemptying process can thus be achieved independently of gravity andmerely as a function of the suction capacity of the pumps. This makes itpossible to shorten the emptying times considerably, reduces theresidual volume remaining in the system and consequently allows asmaller amount of solvents to be used.

[0025] Advantageously, the four-way valve is designed as a disk valve,so as to avoid any dead spaces in which the medium could otherwiseharden in the event of lengthy nonactuation. Irrespective of this, feedand discharge to the pump assembly may also take place from below.

[0026] Advantageously, the housing parts are formed from conductivepolyethylene which has good chemical resistance to a multiplicity ofmedia and, in particular, meets the requirements demanded of materialsfor the use of solvent-containing substances. Furthermore, having aspecific gravity of 0.95, it is light, thus making it easier to handlethe pump assembly.

[0027] The invention is explained in more detail below with reference toan exemplary embodiment illustrated in the drawings in which:

[0028]FIG. 1 shows a top view of the delivery side of the pump assemblyof the system according to the invention;

[0029]FIG. 2 shows a top view of the suction side of the pump assemblyof the system according to the invention;

[0030]FIG. 3 shows a cross section through the feed chamber, includingthe integrated pulsation damper;

[0031]FIG. 4a shows a cross section through the feed chamber along theline A-A of FIG. 3;

[0032]FIG. 4b shows a cross section through the plane B-B of FIG. 4a;

[0033]FIG. 5 shows a cross section through the return chamber of thepump assembly of the system according to the invention;

[0034]FIG. 6 shows a cross section through the return chamber along theline C-C of FIG. 5;

[0035]FIG. 7 shows a diagrammatic illustration of the conveying pathduring the regular operation of the system according to the invention;

[0036]FIG. 8 shows a diagrammatic illustration of the conveying path foremptying the coating system, including the pump assembly, and

[0037]FIG. 9 shows a cross section through the doctor blade chamber.

[0038] The system according to the invention has a drive 1 with acentral compressed-air connection 2 and a return chamber 3 and with afeed chamber 4 which is equipped with an integrated pulsation damper 5.

[0039] The coating medium is conducted via a vertical connection 6 intoan integrated pulsation damper 5 via suction and delivery valves of thefeed chamber which are not illustrated in any more detail. Thispulsation damper has its own control 8.

[0040] After leaving the pulsation damper, the coating medium passesthrough the needle valve 10 via the duct 9 and is conducted into thedoctor blade chamber 14 via the feed line 11.

[0041] A four-way valve 12 on the delivery side of the feed chamber 4makes it possible, by being actuated, for coating media to be sucked infrom the doctor blade chamber 14.

[0042] The return of the coating medium takes place in the doctor bladechamber 14 via a small reservoir 13, the volume of which corresponds tothat of the displacement volume of the diaphragm 15. The coating mediumis administered to the return chamber 3 through the return conveyanceline 17 via the connection 16. The coating medium is subsequentlyconveyed out of the return chamber back into the stock container 7directly via the vertical outlet 18.

[0043] When the system is emptied in the event of a product change,after the changeover of the four-way valve 12 the medium is sucked viathe line 19 into the feed chamber and from there into the stockcontainer. The necessarily corotating return chamber empties the lineand the pump chamber.

1. A system for the circulatory conveyance of media, with two conveyingchambers and with a common drive (1), wherein the first conveyingchamber constitutes a feed chamber (4) and the second conveying chambera return chamber (3).
 2. The system as claimed in claim 1, defined by adouble-diaphragm pump.
 3. The system as claimed in claim 1 or 2, definedby a pulsation damper
 4. The system as claimed in claim 3, wherein thepulsation damper (5) is integrated into the feed chamber (4).
 5. Thesystem as claimed in one of claims 1 to 4, defined by a needle valve(10).
 6. The system as claimed in one of claims 1 to 5, wherein at leastone line connection is arranged perpendicularly to the feed chamber (4)and/or return chamber (3).
 7. The system as claimed in one of claims 1to 6, defined by polyethylene housing parts of the drive (1) and/or ofthe conveying chambers (3,4).
 8. The system as claimed in one of claims1 to 7, defined by a reservoir (13).
 9. The system as claimed in one ofclaims 1 to 8, defined by a four-way valve (12).
 10. The system asclaimed in claim 9, wherein the four-way valve (12) is designed as adisk valve.
 11. A use of a system as claimed in one of claims 1 to 10for the conveyance of media along a circulatory path between a first anda second container.
 12. A use of a system as claimed in one of claims 1to 10 for regulating the filling-level height in a doctor blade chamber.13. A use of a system as claimed in claim 9 or 10 for emptying a firstand a second container.
 14. A method for conveying a medium from a firstcontainer into a second container, with the following steps: operating apump assembly with a feed chamber and with a discharge chamber by meansof a common drive; sucking the medium out of the first container into afeed chamber; discharging the medium from the feed chamber into thesecond container; sucking the medium out of the second container into areturn chamber, and discharging the medium from the return chamber intothe first container.
 15. The method as claimed in claim 14, defined by apulsation damping of the medium.